H.R.13899 - A bill to delay the effective date of certain proposed amendments to the Federal Rules of Criminal Procedure and certain other rules promulgated by the U.S. Supreme Court.94th Congress (1975-1976)

Congress.gov databases include cosponsorship dates (including identification of "original" cosponsors) since 1981 (97th Congress). Prior to 1981, you may be able to find some information online, but often the information is available only in print form.